Covert Transthyretin Amyloidosis Mimicking Advanced Obstructive Hypertrophic Cardiomyopathy Despite Multiple Negative 99mTc-PYP Radionuclide Scans

We present the case of a 74-year-old woman diagnosed with obstructive hypertrophic cardiomyopathy. Amyloidosis was initially considered because she was genotype positive in the transthyretin gene. However, because of 2 negative 99m technetium pyrophosphate radionuclide scans, this diagnosis was considered unlikely, and endomyocardial biopsy was deferred. She had an adverse response to all attempted medical therapies for her left ventricular outflow tract obstruction and ultimately underwent surgical myectomy. Surgical pathology revealed transthyretin (TTR) amyloidosis. This case highlights the limitations of diagnostic testing and reinforces the consideration of more invasive procedures to determine the true underlying cause of disease. This helps clinicians provide the most advanced level of treatment available. TTR amyloidosis can mimic hypertrophic cardiomyopathy with left ventricular outflow tract obstruction. 99m Technetium pyrophosphate scans are useful to investigate the presence of TTR amyloid, but if suspicion persists despite negative testing, it is reasonable to perform an endomyocardial biopsy.